Currently, most charge coupled devices (CCD) sensors are packaged in multilayer high temperature cofired ceramic dual-in-line packages. Multilayer ceramic packages have traditionally been used for the packaging of power devices or UV erasable memories. With the advent of Camcorders, and fax machines, the multilayer ceramic dual-in-line package has been extended to the packaging of low end charge coupled devices. The multilayer ceramic structure has many advantages when packaging CCDs. Multilayer ceramic dual-in-line (DIP) packages have the following desirable properties: 1) low moisture permeability; 2) high dimensional stability; 3) a temperature coefficient of expansion closely matching silicon; 4) good thermal conductivity; 5) infrastructure is in place for high volume manufacturing; and 6) testability;
The major disadvantages of the ceramic dual-in-line package is the cost, and to a lesser extent, the obsolescence issues surrounding the integrated circuit packaging industry moves away from dual-in-line package and toward surface mount technology.
Another key disadvantage concerns the alignment of the CCD to the imaging and viewfinder optics; as one finds in digital cameras. The alignment of the CCD to the lens system requires that the CCD be precisely positioned to the optical axis, and the focal plane of the lens. Unfortunately, the positional variability associated with the location of the dual-in-line package pins is so large that it is impractical to use these pins as mechanical reference to the CCD device. Consequently, other reference datums must be created. The dual-in-line package pins then become an additional mechanical constraint on the mechanical design. The pins while compliant are sufficiently rigid to require that additional compliance be added to the mechanical design of the system. Flexible circuits are often used to overcome the mechanical constraints imposed by the dual-in-line package pins. Typically, the flexible circuit is connected directly to the dual-in-line package. In other cases, the dual-in-line package is mounted to a circuit board, and the circuit board is then connected to the system electronics with a flexible interconnect.
Still another disadvantage of the dual-in-line package is the inability to automate the assembly of the CCD device into the product level assembly. The temperature sensitivity of the charge coupled device means that standard automated electronic assembly techniques; such as, solder reflow ovens, or wave-soldering can not be used when assembling the dual-in-line package to the system electronics. Often, a hand-soldering operation is required to interconnect the dual-in-line package to the system electronics. Elimination of the need to hand solder these connections increases the quality of the entire system.
As can be seen from the foregoing description, there remains a need within the art for a CCD packaging that can cure the previously discussed problems within the prior art.